1. Field of the Invention
The present invention relates to a magnetoresistive effect element and a manufacturing method thereof, and a magnetic head, a magnetic reproducing apparatus, and a magnetic memory using the mangetresistive effect element.
2. Description of the Related Art
Sensitivity improvement of a GMR (Giant Magnetoresistive Effect) head supporting a magnetic recording density of an HDD (Hard Disk Drive) is near to reach a limit. A renewed high sensitive reproducing head becomes necessary to increase a recording density over 100 gigabits per one square inch. A GMR head making use of a tunnel effect (TMR (Tunneling Magnetoresistive Effect) head) can be cited as one candidate thereof. However, the TMR head also includes a principle problem that resistance increases in accordance with the increase of the recording density.
A GMR head having so-called a CPP (Current Perpendicular to Plane) structure in which a sense current is passed in a film plane perpendicular direction of a magnetoresistive effect film is expectable, to realize the recording density of 200 gigabits or more. According to the GMR head having the CPP structure, it is possible to obtain an MR change ratio of approximately 10 times of a CIP (Current in Plane) structure. Further, the GMR head having the CPP structure also has an advantage that the resistance thereof is low compared to the TMR head.
However, even in the CPP type GMR head, a resistance change ratio thereof remains in approximately 15% at maximum, and a limit of the resistance change ratio in principle is also considered to be approximately several 10%. A miniaturization of recording bits is advanced owing to the increase of the recording density in a magnetic recording field. As a result, it becomes difficult to obtain sufficient signal strength. Consequently, magnetoresistive effect material with higher sensitivity is expected, and a requirement for the GMR head showing a larger resistance change ratio goes higher and higher.
Recently, a magnetic microcontact in which two acicular nickels are faced, or a magnetic microcontact in which two magnetites are brought into contact is reported as the magnetoresistive effect material showing the resistance change ratio of 100% or more. These materials show the large resistance change ratio, but every magnetic microcontact is created by facing two ferromagnetic materials processed into acicular states or triangle states. Therefore, it is difficult to apply to a practical GMR head as it is. Further, a magnetic microcontact in which two slim nickel wires are disposed in T-shape and a micro column is grown at a contact portion by using an electrodeposition method is reported. It is also difficult to apply this magnetic microcontact to the GMR head.
There are many opinions as for a beginning of the large resistance change ratio resulting from the magnetic microcontact, but a ballistic conduction effect at a contact portion can be cited as one of the beginning. It is conceivable that the magnetic microcontact exhibits an extremely large magnetoresistive effect (Ballistic Magnetoresistive Effect (BMR)) by generating a ballistic conduction between magnetic layers. In a manufacturing process of a spin-valve film in which the nonmagnetic intermediate layer is interposed between two ferromagnetic layers (magnetization pinned layer and magnetization free layer), a process becomes necessary to constitute a nonmagnetic intermediate layer practically with an insulator, and to form at least one micromagnetic region of nano-size within a part of the nonmagnetic intermediate layer to apply the above-stated BMR to a magnetic head.
When the micromagnetic region is formed by a normal lithography process, the minimum size thereof remains to be at approximately 10 nm even though an electron-beam lithography apparatus capable of realizing the finest pattern is used. Accordingly, it is difficult to create the micromagnetic region (magnetic point contact) with the size of several nm required for the exhibition of the BMR. In JP-A 2003-204095 (KOKAI), it is described that a hole with a maximum width of 20 nm or less is provided at an insulating layer disposed between a magnetization pinned layer and a magnetization free layer, and a magnetic microcontact is formed by filling a ferromagnetic material in the hole. However, it is difficult to form the magnetic microcontact capable of exhibiting the BMR with good repeatability by using the method as stated above.
The magnetic microcontact has a possibility to show a large magnetoresistive change ratio. However, the conventional magnetic microcontact has a structure in which a precise control at the time of creation is difficult, and further, a structure which is difficult to apply to the magnetic head. It is necessary to develop a structure and a manufacturing method of the magnetic microcontact capable of mass production and having good controllability to apply the BMR based on the magnetic microcontact to the magnetic head and so on.